1. Field of the Invention
The present invention relates to the field of dissipating the heat from electronic components on printed circuits, and its subject-matter is more particularly a method for fabricating an electronics board with thermal-conduction cooling.
2. Discussion of the Background
In the electronics components sector, integrated circuits are nowadays becoming smaller and smaller, while fulfilling increasingly complex functions. The rise in the integration density leads to an increase in the density of heat dissipated in the units containing the electronics boards, the physical dimensions of which are still of the same order of magnitude. Problems then arise with removing the energy dissipated as heat during their operation.
The effect of this is that, as the dimensions of the integrated circuits decrease, it becomes increasingly difficult and expensive to resolve the problems posed by thermal dissipation. Because of economic problems, the electronics industry, with essentially military applications, is diversifying into the civil industrial sector.
A great expansion of electronics hardware is currently being observed in the civil industrial sector, which in functional terms today rivals some military hardware.
In order to use boards designed initially for civil uses, it is then necessary to deal with environmental constraint and climatic constraint problems which are more severe in the military field than in the civil field.
Electronics components fabricators always specify a maximum operating temperature, above which the characteristics of the component are no longer guaranteed. Depending on the function of the component and its field of application, the maximum temperature varies from +70.degree. C. for the industrial range to +125.degree. C. for the military range. In order to use components which were initially provided for operation at a maximum temperature of 70.degree. C., and are now intended to operate at a higher temperature, it is necessary to have local cooling of the electronics board equipped with the components.
Local cooling makes it possible to maintain an operating temperature which is compatible with the maximum allowable temperature for normal use of the board.
In order to promote the dissipation of heat from components wired on a printed circuit, it is known to use a conductive heat-transfer device placed between the components and the cover of the metal unit containing the board equipped with the components, the cover being used as a dissipative cooling plate.
In one known embodiment, a plastic sachet containing a coolant of the "fluoradiator" type is used; a sachet of this type is marketed under the brand name Fluorinert.
A thermal dissipation device of this type is difficult to use in devices which contain a plurality of boards, for example board racks fitted to bay structures. This is because the boards are generally positioned vertically inside the rack, and the small space between the boards does not allow a dissipative cold plate to be inserted. Furthermore, because of the vertical position of the boards, a device of the cooling-sachet type could no longer be held on the board. Finally, the sachet-type device is fairly stiff and can only fit on the top of those electrical components which protrude furthest from the printed circuit board. The interface between the components and the sachet is not optimized. It is thus not possible for some of the components, which are not in contact with the sachet, to be cooled sufficiently to allow them to operate in the temperature ranges specified for military applications. This means that boards equipped in this way are ruled out from these applications.
In order to resolve this problem and to allow the use of any commercial board for military uses, the applicant company has described, in French Patent Application No. 92 06041 filed on May 19, 1992 and published on Nov. 26, 1993 under U.S. Pat. No. 2,691,604, a method which consists in forming, on any board equipped with components, a rigid heat sink which is fixed to the board, matches the components as closely as possible and thus allows them to be cooled, even for the highest temperatures in the military range, it being possible for the board to be used in hardware which includes board racks.
To this end, this method uses a system for taking a scan of the face on which the electronic components are located, or of an impression of this face, which uses a mechanical sensor whose precision, robustness and scanning speed are mediocre.